Feasibility study of looped-catheter-based 2d-3d image registration of CT and x-rays for cardiac catheterization procedures in a phantom experiment

For X-ray guided cardiac catheterisations it is desirable to overlay pre-operative 3D-CT information for additional guidance. A common technique to obtain an overlay is to loop a catheter inside a target chamber and then manually align CT-derived surface models using multiple X-ray views. We propose and test a fully automatic algorithm for this purpose. The algorithm aligns the images by first estimating the pose of the CT relative to the X-ray table using the supine and isocentre constraints. Subsequently the pose is refined using an iterative optimisation strategy that maximises the intersection between the loop and projected target chamber, while minimising the separation between the X-ray cardiac border and the projected ventricles, in two X-ray views. Validation was carried out using a geometrically-realistic plastic heart phantom with two looped-catheter configurations formed inside the left atrium. The algorithm executes in under five minutes and yields average 3D-TREs between 2.4 and 5.4 mm over various regions of the heart, and 4.0 mm over the four chambers. Preliminary evaluation of this novel approach indicates feasibility for clinical interventional guidance and merits thorough validation using further phantom and clinical images.